The present invention is generally related to the field of mass media information storage devices, and more particularly to circuits for controlling the write current used to drive a thin film write head.
Hard disk drives are mass storage devices that include a magnetic storage media, e.g. rotating disks or platters, a spindle motor, read/write heads, an actuator, a pre-amplifier, a read channel, a write channel, a servo circuit, and control circuitry to control the operation of hard disk drive and to properly interface the hard disk drive to a host system or bus. FIG. 1 shows an example of a prior art disk drive mass storage system 10. Disk drive system 10 interfaces with and exchanges data with a host 32 during read and write operations. Disk drive system 10 includes a number of rotating platters 12 mounted on a base 14. The platters 12 are used to store data that is represented as magnetic transitions on the magnetic platters, with each platter 12 coupleable to a head 16 which transfers data to and from a preamplifier 26. The preamp 26 is coupled to a synchronously sampled data (SSD) channel 28 comprising a read channel and a write channel, and a control circuit 30. SSD channel 28 and control circuit 30 are used to process data being read from and written to platters 12, and to control the various operations of disk drive mass storage system 10. Host 32 exchanges digital data with control circuit 30.
Data is stored and retrieved from each side of the magnetic platters 12 by heads 16 which comprise a read head 18 and a write head 20 at the tip thereof. The conventional readhead 18 and writehead 20 comprise magneto-resistive heads adapted to read or write data from/to platters 12 when current is passed through them. Heads 16 are coupled to preamplifier 26 that serves as an interface between read/write heads 18/20 of disk/head assembly 10 and SSD channel 28. The preamp 26 provides amplification to the waveform data signals as needed. A preamp 26 may comprise a single chip containing a reader amplifier 27, a writer amplifier, fault detection circuitry, and a serial port, for example. Alternatively, the preamp 26 may comprise separate components rather than residing on a single chip.
Particular areas for improvements of write driver current circuits used to drive a thin film head include addressing the inaccuracies of the write current, and providing the ability to change the write currents waveform shape so that customers of these circuits can customize the disk drive performance with many variations of thin film write heads provided by different suppliers. That is, there are several available thin film write heads manufactured in the industry, each having it""s own drive characteristics and each interfacing slightly differently to the available write drive circuits. Accordingly, there is desired an improved write driver current circuit which can provide both an accurate selectable write current, and which write current can have parameters selectively customized for optimizing disk drive performance.
The present invention achieves technical advantages as a write current driver circuit adapted to both selectively establish an amplitude of the write current signal, and which tracks multiple variations including process, supply voltages and temperatures, and in addition can be selectively controlled and programmed to control the amplitude, overshoot amplitude, and overshoot duration.
Preferably, the write current driver circuit includes a write current reference voltage circuit, which is adapted to selectively establish amplitude of the write current. Preferably, the write current reference voltage circuit is adapted to set a DC write current to the write head. A very accurate write current can be established and selectively provided to compensate for variations in process, supply voltages and temperature. The write current reference voltage circuit preferably includes a feedback loop feeding back transistor current to achieve loop stability, and preferably includes a feed forward capacitor adapted to stabilize the feedback loop.
A plurality of transistors are provided to control multiple parameters of the write current. Preferably, a first set of transistors provides a boost current to produce a write current overshoot. A second set of transistors provides a differential write data signal. An overshoot amplitude of the write current is programmable by creating a pulsing signal. Using the original differential write data signal and a programmable delay version of the write data generates this signal. Preferably, the pulsing signal""s current amplitude is also programmable by a programmable current source. These transistors are preferably biased with a trickle current to increase transient switching time. Moreover, these trickle currents are compensated for in the write current reference voltage circuit to maintain write current accuracy. Preferably, PMOS transistors are provided to control the boost currents and the differential write data signals.